1. Field of the Invention
The present invention relates to an image interpolation device for changing a frame rate of dynamic-image signals, especially, for conducting frame interpolations, and a frame rate converter and image display apparatus using the image interpolation device.
2. Description of the Related Art
Currently, there are a variety of specifications concerning image signals such as the video signals used for video media and for personal computers (PCs). In general, the image signals defined by the Video Electronics Standards Association (VESA) are widely known, and image formats as many as several types varying in frame rate are defined, even for the VESA standards signals. Unlike this, the kind of image format to be used for display is usually fixed for image display apparatus such as plasma display panels (PDPs) and liquid-crystal displays (LCDs). Therefore, to apply image signals of one of the above-mentioned various image formats to such image display apparatus, it is necessary to convert that image format into a format appropriate for the image display apparatus, and a device that suits this purpose is desired.
In general, when the frame rate of dynamic images is converted, an interpolation processing is carried out in which an interpolation frame is interpolated between original frames of the image signal. As the frame interpolation method, a method based on motion compensation processing which utilizes frame-to-frame motion vectors with attention focused on the current frame and on the previous frame is known. In this method, the motion between frames is identified from motion vector information and an interpolation frame is created using the information.
Several methods are proposed in order to enhance the accuracy of motion vectors in such interpolation. These methods involve, for example, searching for motion vectors in search areas of two split levels, or conducting a smoothing process for removal of inappropriate motion vectors, based on comparisons with respect to surrounding motion vectors (refer to Japanese Patent Laid-open No. 2002-27414, for example).